This invention relates generally to medical imaging systems, and more particularly to attenuation correction for medical imaging.
A nodule found during a CT scan often requires a patient to return many months later and obtain another CT scan to determine malignancy based on a nodule doubling time. PET scans may be helpful in diagnosis due to increased metabolic activity in the region of the nodule. However, due to the comparatively lower resolution of PET images as compared to CT images, and due to the effects of respiratory or patient motion during a PET scan, nodule activity can be blurred in the PET scan. Consequently, it can be difficult to quantify the nodule activity with a PET scan alone, which may result in an indeterminate or incorrect outcome of the diagnosis of the nodule.
The image quality of at least some known PET and CT is highly affected by physiological patient moving. Such image quality may affect diagnosis. Lung nodules, cardiac wall features or other small features of interest that move due to physiological motion such as cardiac and respiratory motion, may appear unfocused or faint without proper corrections. Misalignment of the CT attenuation map and PET emission image due to respiratory motion may cause errors in the attenuation correction (AC) factors and may produce artifacts in the final reconstructed AC PET image. For instance, a recent proposal suggests “under attenuation correction” has the potential of introducing artifacts that resemble artificial myocardial perfusion defects in cardiac PET. Thus, in the case of cardiac PET, attenuation artifacts may result in artificial visual depressions in the myocardial wall that may be incorrectly interpreted as perfusion defects by utilizing cine CT attenuation correction (CTAC) data.